temp reg in ectotherms - exam 4

ectotherms

animals that need to obtain heat from sources outside their body for body temps to be raised

• there is heat produced via metabolic processes and skeletal muscle contraction, but not enough to maintain their body temp

heat balance

heat gain + heat lost

• gain heat by internal processes and external processes

• the amount of heat an ectotherm can produce internally is always smaller than heat lost → requires an external mechanisms to maintain heat balance

heat balance in water vs. land

heat lost more quickly in water versus land (23x faster!!)

• thermal conductivity of water is much greater than air

• respiration rate of animals also higher in water versus air (increased effect of convection)

  • less oxygen in water

  • must respire more often to meet oxygen demands

  • losing/gaining heat much faster

thermoconformer

matching external environment heat

• many aquatic ectotherms do this

behavioral thermoregulation

• animal changes its behavior to influence their body temp

• typically done through thermal selection/habitat selection

  • thermal selection can only work if there is a diversity of environmental temperatures (more variation in temp in a terrestrial environment versus an aquatic one)

preferred body temperature

temperature that optimizes physiological performance of an organism

• habitat selection with coincide with this temp

changes in body temperature demand

preferred body temperature may change seasonally, yearly, or throughout the day!

• based on physiological demand

ex. digestion, reproduction, growth status

shuttle thermoregulation

typically, heat gain due to insolation (solar radiation) followed by heat loss in cooler habitat due to conduction, convection, evaporative water loss

• overall, there is a net heat balance (brings body temp above and then lowered → net balance coincides with preferred body temp)

• requires temperature receptors with two set points to drive behavior

• will not work for amphibians due to their high skin permeability

effect of body size

surface area to volume ratio → bigger animals lose less heat compared to smaller animals proportionally

• SA does not increase proportionally as size increases

thermophilic animals

active at temperatures exceeding 45°C

• do this but using extreme shuttling behaviors

• not always experiencing 45°C

• very little conduction by holding itself further from ground

adaptive benefits:

• eat all the dead

• avoid all the predators

peripheral thermoreceptors

receptors on outside of a cockroaches body that allow for them to detect the thermal environment and respond to it

• feel their way through environment to select preferred temp

internal thermoreceptors

change firing rate based on temperature → thermal gated channels are triggered

• typically found in hypothalamus

• another way for organisms to detect the thermal environment

other ways to thermoregulate

• changes in pigmentation

• changes in blood flowing to surface tissues

• respiratory cooling by evaporative water loss

surviving the cold and subzero conditions

latitudes closer to poles experience seasonal temperatures

• when seasonal temps become too cold: migrate, overwinter

migration

organism moves to warmer climate to survive cold conditions of natural habitat

overwinter

organisms stay in cold and subzero conditions and adapt new strategies to survive

aestivation

resting or dormant period during summer or drought

• in endotherms it is a controlled hypothermia during summer

hibernation

resting or dormant period during winter

• endotherms: a controlled hypothermia

metabolic suppression

controlled suppression of metabolic rate to some scale

dispause

reduction in metabolic rates by about a factor of 10

• so extreme that it is mostly restricted to invertebrates (mainly insects)

insect diapause

mostly restricted to insects

• biochemical reactions slow, but do not stop

• stored energy (lipids and carbs) meet energy demands

• aerobic metabolism still used

  • only need a little oxygen

  • never tap into anaerobic metabolism

  • large amount of waste builds up → causes harmful effects

• dispause is not a direct response to temperature, but likely “planned” event based on photoperiod changes

• insects may enter dispause at different stages (egg, pupae, larvae, adult)

diapause hormones

photoperiod cues initiate this in insects

• photoperiod aligned with seasonal shifts in food resources

• impact of climate change: food sources may change when available and no longer correlate with diapause

hibernaculum

site of hibernation for amphibians and reptiles

• photoperiod can no longer be used

• temperature is a major cue (ex. ice forming thermal blanket)

• hibernaculum choice important

• become thermoconformers to cope with colder temps

survival through hibernation

1. sufficient energy stores

2. sufficient oxygen availability

   • anaerobic metabolism can only be used sparingly (effects of lactic acid build-up)

   • metabolic suppression used to slightly lower metabolic activity

freeze-tolerant ectotherms

use supercooling → go below freezing w/o forming ice, rather formation of crystals in ECF that will then release heat and increase temp of body

• once “internal fluid” has frozen, animal can survive upward of -50 to -80℃

  • freeze tolerance varies among species

• promotion of crystallization in ECF is essential b/c ice crystallization in ISF will rupture cell

free tolerance mechanism

ECF will freeze, removing solvent without removing the solutes

• this will increase osmolarity of ECF (prior ISF and ECF were isotonic)

• following flow-down gradient, solutes will move out of cell and increase osmolarity of inside cell (dehydrating it)

• increasing osmolarity of ISF will lower freezing point of cell → promote freezing of ECF by making sure cell will not freeze until you get to a rlly low temp

encourages ECF freezing

ice-nucleating agents and cryprotectants

ice-nucleating agents

proteins in ECF that encourage ice formation (slow ice formation)

• ice will form around them very slowly

• coupled with cryoprotectants

cryoprotectants

proteins that protect tissues from damage caused by freezing (inhibits)

• ECF cryoprotectants: decrease freezing point and slows freezing

• ICF cryoprotectants: increases osmolarity (acts as a solute) and limits cell shrinkage

coupled with ice-nucleating agents

freeze-tolerant ectotherms

once frozen, cell metabolism is completely anaerobic

• all CR ceases, shuts off means of stuff getting in/out b/c ECF is frozen

freeze avoidance

avoidance of ice crystallization completely

1. supercooling

2. antifreeze compounds

these methods are used in compound w/ e/o

supercooling

animal must cool slowly and clear all ice-nucleating agents

colligative antifreezes

lower freezing point as they act as solutes, increasing osmolarity

• small molecules (glycerol, urea, TMAO)

  • diffuse out of resp surface and ultrafiltration

  • large metabolic demand b/c they are constantly lost to environment

non-colligative antifreezes

specialized molecules that adhere to and suppress the growth of ice crystals

• ex. found in Antarctic fish who live in ice sheaths